The long-term goal of this research is to elucidate the molecular and cellular mechanisms that ensure potassium (K+) channels assemble with the appropriate membrane-embedded regulatory subunits for proper physiological function. The KCNE regulatory subunits are a class of type 1 transmembrane peptides that co-assemble with tetrameric voltage-gated K+ channels, providing the electrical diversity needed to function in a wide-variety of cells and tissues. This proposal investigates KCNQ1-KCNE K+ channel complexes that enable potassium ingress into the endolymph, maintain salt and water homeostasis in intestinal epithelia, and generate the cardiac IKs current. There are three aims to this proposal: (1) We will establish assembly mechanisms for K+ channel-KCNE complexes with structurally different tetramerization domains and determine how the disease-associated mutations directly affect co-assembly. (2) We will determine the quaternary structures of misassembled K+ channel subunits in the endoplasmic reticulum. (3) We will determine whether KCNE subunits asymmetrically modulate the ion-conducting subunits using a combination of derivatized scorpion toxins and differentially-mutated KCNQ1 subunits.